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The performance of the ultraviolet telescope (UVIT) on-board AstroSat is reported. The performance in orbit is also compared with estimates made from the calibrations done on the ground. The sensitivity is found to be within $$\sim $$ 15% of the estimates, and the spatial resolution in the NUV is found to exceed significantly the design value of $$1.8^{\prime \prime }$$ and it is marginally better in the FUV. Images obtained from UVIT are presented to illustrate the details revealed by the high spatial resolution. The potential of multi-band observations in the ultraviolet with high spatial resolution is illustrated by some results. [ABSTRACT FROM AUTHOR]

The UVIT telescopes are a payload package on the ISRO Astrosat observatory. They are co-aligned with three X-ray telescopes, and will operate simultaneously with them. The overall observatory is summarized, and details are given of the design, performance, and operation of the UVIT telescopes. These will offer close to arcsecond resolution over half-degree fields, simultaneously in FUV, NUV, and blue-visible bands. All bands have several filters and the UV bands have low-dispersion objective gratings. [ABSTRACT FROM AUTHOR]

The AstroSat satellite is designed for multi-wavelength astronomy for observations covering a spectral range from soft and hard X-rays to the ultra-violet. The Ultraviolet Imaging Telescope (UVIT) is the only non-X-ray telescope on AstroSat and it provides the long lever arm to the multi-wavelength observations. In addition to the simultaneous multi-wavelength studies in coordination with the X-ray telescopes on-board AstroSat, UVIT is used to study a large variety of objects with arcsecond-level spatial resolution. During the first year of observations, UVIT has obtained images in many filter bands in the wavelength range 130-300 nm over a field of ~28', which are being used to study a variety of hot stars, nebulae, stellar clusters and galaxies. [ABSTRACT FROM AUTHOR]

Context. Some post-merger galaxies are known to undergo a starburst phase that quickly depletes the gas reservoir and turns it into a red-sequence galaxy, though the details are still unclear. Aims. Here we explore the pattern of recent star formation in the central region of the post-merger galaxy NGC7252 using highresolution ultraviolet (UV) images from the UVIT on ASTROSAT. Methods. The UVIT images with 1.2 and 1.4 arcsec resolution in the FUV and NUV are used to construct a FUV-NUV colour map of the central region. Results. The FUV-NUV pixel colour map for this canonical post-merger galaxy reveals a blue circumnuclear ring of diameter ~1000 (3.2 kpc) with bluer patches located over the ring. Based on a comparison to single stellar population models, we show that the ring is comprised of stellar populations with ages ≲300 Myr, with embedded star-forming clumps of younger age (≲150Myr). Conclusions. The suppressed star formation in the central region, along with the recent finding of a large amount of ionised gas, leads us to speculate that this ring may be connected to past feedback from a central super-massive black hole that has ionised the hydrogen gas in the central ~400 ~1:3 kpc. [ABSTRACT FROM AUTHOR]